In one known device of this type (shown in German Pat. No. 1,293,563) a water jet nozzle having its outlet directed perpendicular to the plane of the web is moved across the web, together with its supply pipe, by means of a roller chain. This device is complicated and prone to breakdown. That is why it is used only to a limited degree in paper cutting machines.
With paper cutting machines, the paper web is "beat loose," i.e., cut, only if the web is torn off somewhere in the machine. In this case the web normally is beat loose on the first free pull, i.e., the part of the path of travel of the web at which it runs for the first time without any support from a filter, a felt layer or a roller. At the beat-loose point, the subsequent length of fiber web that is being fed from the headbox runs into a bin until the machine ends (press ends, dry ends, etc.) are ready again for operation.
Because of the drawbacks of the known water nozzle devices, the paper web normally is beat loose either by an operator, who cuts the web loose by hand, or by an immovably positioned air jet, which is directed from the side of the paper web against the lengthwise edge of the web. Only the lengthwise edge of the paper web is torn off, and the paper web thereafter completes tearing itself apart. But, this is successful only with a thin type of paper web having only a slightly longitudinal fiber direction. With webs having greater longitudinal strength, there is a danger that after the web is cut inwardly only partway across its width, the web will thereafter continue to tear in a longitudinal direction. Another drawback is that the beat loose web end frequently curls up. This produces a multiple web thickness that runs through subsequent pressure slits of the paper cutting machine. The pressure slits are defined between opposed pressure rollers and the slits contain filters or, felt layers, and the thick, multi-layer web can damage them as well as the pressure rollers. The web may shred in the pressure slits, and scraps of the web will have to be removed. This results in extensive down time for the exchanging of filters and, in the case of peripheral groove equipped press rollers, for the cleaning of the grooves.